Conventional vehicle transmissions predominantly employ wet clutches to accomplish gear shifting. Transmissions typically include a transmission fluid which is recycled throughout the transmission. Wet clutches generally provide greater heat transfer and temperature control than dry clutches. Wet clutches also, however, have a lower coefficient of friction than dry clutches. Wet clutches are further known to slip pre-engagement as wet clutches have a lower coefficient of friction.
Dry clutches tend to provide higher coefficients of friction than wet clutches. Dry clutches can provide lower costs and complexity. Still, dry clutches can have thermal management and durability issues. Some powershift dry dual-clutch transmissions (or “DCTs”) comprise a manual clutch construction, e.g., as disclosed in U.S. Patent Publication No. 2010/0113216 titled “Temperature Control of Dual Input Clutch Transmission.” Two clutches are utilized to provide functionality closer to that of an automatic transmission clutch vehicle launch. Temperature can significantly impact the length of service life of a transmission in which each input clutch is a dry clutch. A friction surface—the primary source of heat for the transmission—is surrounded by material and lacks a direct convection path for cooling. The transmission has heavy components with high inertia and low heat dissipation. Though the use of a controlled fan can improve cooling in the transmission, the indirect air flow path from the fan to the heat source slows down the cooling process.
Another common issue in dry-clutch transmissions is that clutch wear can be significantly increased by high operating temperatures. Repetitive engagement of clutch components can cause wear on the friction plate. This wear can decrease clutch lifespan. Some existing transmissions have a clutch adjustment mechanism that iteratively adjusts the position of the pressure plate when the clutch becomes slow to engage. Once a maximum distance for clutch engagement is detected the system moves clutch components into a tighter relative position. Since the adjustment is stepwise, the system repetitively over- and under-adjusts both after adjustment and before re-adjustment, respectively. A more efficient method of clutch adjustment is desired. Additionally, a more robust and reversible design is preferred.
Therefore, it is desirable to have a dry-clutch transmission with improved durability and wear reduction techniques. Cooling techniques which provide a more direct convection and conductive path are needed to reduce overheating in the transmission. Moreover, a continuously variable clutch wear compensation assembly is desirable to have a more flexible yet, effective and robust clutch wear adjustment mechanism.